The present invention relates to a liquid material supply apparatus and method for supplying a liquid material to a deposition chamber.
Generally a semiconductor device fabrication process includes depositing films on semiconductor wafers, etching the wafers by micronized processing techniques, and other treatments. By repeating these operations, films are deposited in multi-layers on the wafers.
To deposit films on semiconductor wafers, generally CVD (Chemical Vapor Deposition) apparatuses, sputtering apparatuses, etc. are used. Here, to give an example, the deposition of films by a CVD apparatus will be explained. Semiconductor wafers are placed in a deposition chamber the interior of which is in a vacuum or under the normal pressure. A required deposition gas is supplied into the deposition chamber with the wafers set at a required processing temperature, and a reaction product produced by, e.g., a chemical reaction is deposited on the surfaces of the wafers.
Processing gases used in this film deposition are, e.g., halogen compounds, such as WF.sub.6, TiCl.sub.4, etc., which are formed by compounding deposition metals with halogen. These compounds are gaseous at the normal temperature and under the normal pressure. In supplying the processing gases, the processing gases which are loaded in processing gas bombs under a primary pressure of, e.g., about 150 kg/cm.sup.2 are unloaded out of the bombs down to a secondary pressure of, e.g., 2-5 kg/cm.sup.2, and the processing gasses are controlled by a mass flow controller for controlling mass flow rates of the gases provided in a gas box near the deposition chamber to be supplied into the deposition chamber.
For the above-described gaseous deposition materials, the so-called low vapor pressure liquid materials, that are liquid at the normal temperature and under the normal pressure have been recently developed. Such liquid materials presently tend to be more used because of very good film characteristics of their deposited films. The low vapor pressure liquid materials comprise organic metal materials, e.g., diethylaminotitanium (Ti[N(C.sub.2 H.sub.3).sub.2 ].sub.4, trimethylvinylsilylhexafluoroacetylacetate copper (I) (Cu.sub.8 hfac)vtms), etc. These materials are harmful to the human body and have a property that they are very reactive and readily oxidized upon contact with air.
To supply the low vapor pressure liquid materials into the deposition chamber, the supply systems for the deposition gases cannot be used because the liquid materials are liquid at the normal temperature and under the normal atmosphere as described above, and are accordingly difficult to evaporate. In view of this, in place of the supply systems are considered systems of bubbling the liquid materials on carriers gases, such as N.sub.2 gas, etc. to supply them in mist, or systems of heating the liquid materials to supply them in large amounts of vapor.
But the bubbling system has not only a problem that the supply amount is unstable due to changes in liquid amounts and liquid surface areas, and others, but also a problem that the liquid materials are so difficult to evaporate as described above that the bubbling alone cannot secure sufficient vapor amounts.
In addition, another problem is that N.sub.2 gas and H.sub.2 gas used in the bubbling are solved even in traces into the liquid materials to be impurities and affect film deposition on wafers.
The heating system can secure necessary vapor amounts, but has a problem that heating of the liquid materials thermally decomposes and modifies the materials themselves.
Furthermore, both systems have problems that the liquid materials which have been once evaporated again liquefy and that residual liquid materials in pipes and connections react with oxygen and produce solid byproducts on replacement of liquid tanks loaded with the liquid materials, and the solid byproducts clog the pipes and connections.
In addition, the liquid materials are supplied into the deposition chamber finally in gases. Their volumes are accordingly much expanded, but their used amounts per hour are small in liquid amounts. In a piping for the liquid materials constituted by pipes of the usual sizes for gases, the material liquids reside longer and are more susceptible to metal contamination of materials of the pipes.
Thus it has been very difficult to supply stably and accurately the low vapor pressure liquid materials from the liquid tank to the deposition chamber.